The invention relates to a process for treating the petroleum residue from a refinery by an integrated process of thermal cracking and partial oxidation to obtain higher thermal cracking at reduced investment cost.
The residue from a refinery usually comprises the components boiling above about 500-575.degree. C. These residues may comprise any such streams such as vacuum tower residue, visbreaker residue and deasphalting residue. There is a considerable amount of residue from a refinery to be treated. For example, a typical refinery processing 10 million metric tons annually (MTA) of Arabian Mix Crude will produce about 6,500-7,000 MT per stream day (SD) of vacuum tower residue. This residue can be blended into residual fuel oil (which has a low value), upgraded to high value transportation fuels (which is expensive) or gasified to produce power. Without further processing, gasification of this residue will provide about 1,200 MW of electrical power. This is greatly in excess of the amount of power which can be effectively used in the plant. Several processes are available to reduce the amount of the residue but the degree of conversion of the residue is low and/or the cost is high. Examples are:
Cost of Wt % Unconverted Upgrading Plant Process Residue or Coke Formed $ MM Visbreaking 84.5% $ 29.7 Visbreaking & 66.5% $ 38.6 Vacuum Flasher Deasphalting 43.2% $ 46.0 Delayed Coking 32.5% $144.3
Conversions of more than 50% are desired for efficient and effective plant operation but the cost for obtaining such conversions with these prior art processes is high. With respect to visbreaking, the overall conversion to 500.degree. C. and lighter components is limited to 35% in order to maintain the stability of the residue (500.degree. C.+components) for fuel oil blending. Also, the visbreaking process is limited by the maximum skin temperature of the furnace tubes of about 650.degree. C. Although higher yields are possible with visbreaking, the unstable nature of the fuel product and the coking of the tubes pose significant problems. Although the Eureka Process (steam cracking with superheated steam) has a good conversion (67%), it requires the injection of superheated steam to suppress coking which all has to be condensed in a downstream fractionator and then treated in a sour water stripping unit. This adds cost to the unit.